1. Field of the Invention
This invention relates to a technique for driving a plasma display panel, and more particularly to a plasma display panel driving method and apparatus that is capable of driving a plasma display panel at a higher speed as well as improving the contrast.
2. Description of the Related Art
Generally, a plasma display panel (PDP) radiates a fluorescent body by an ultraviolet with a wavelength of 147 nm generated during a discharge of He+Xe or Ne+Xe gas to thereby display a picture including characters and graphics. Such a PDP is easy to be made into a thin-film and large-dimension type. Moreover, the PDP provides a very improved picture quality owing to a recent technical development. Particularly, a three-electrode, alternating current (AC) surface-discharge type PDP has advantages of a low-voltage driving and a long life in that it can lower a voltage required for a discharge using wall charges accumulated on the surface thereof during the discharge and protect the electrodes from a sputtering caused by the discharge.
Referring to FIG. 1, a discharge cell of the three-electrode, AC surface-discharge PDP includes a scanning/sustaining electrode 30Y and a common sustaining electrode 30Z formed on an upper substrate 10, and an address electrode 20X formed on a lower substrate 18.
The scanning/sustaining electrode 30Y and the common sustaining electrode 30Z include a transparent electrode 12Y or 12Z, and a metal bus electrode 13Y or 13Z having a smaller line width than the transparent electrode 12Y or 12Z and provided at one edge of the transparent electrode, respectively. The transparent electrodes 12Y and 12Z are formed from indium-tin-oxide (ITO) on the upper substrate 10. The metal bus electrodes 13Y and 13Z are formed from a metal such as chrome (Cr), etc. on the transparent electrodes 12Y and 12Z so as to reduce a voltage drop caused by the transparent electrodes 12Y and 12Z having a high resistance. On the upper substrate 10 provided with the scanning/sustaining electrode 30Y and the common sustaining electrode 30Z, an upper dielectric layer 14 and a protective film 16 are disposed. Wall charges generated upon plasma discharge are accumulated in the upper dielectric layer 14. The protective film 16 protects the upper dielectric layer 14 from a sputtering generated during the plasma discharge and improves the emission efficiency of secondary electrons. This protective film 16 is usually made from MgO. The address electrode 20X is formed in a direction crossing the scanning/sustaining electrode 30Y and the common sustaining electrode 30Z. A lower dielectric layer 22 and barrier ribs 24 are formed on the lower substrate 18 provided with the address electrode 20X. A fluorescent material layer 26 is coated on the surfaces of the lower dielectric layer 22 and the barrier ribs 24. The barrier ribs 24 are formed in parallel to the address electrode 20X to divide the discharge cell physically and prevent an ultraviolet ray and a visible light generated by the discharge from being leaked into the adjacent discharge cells. The fluorescent material layer 26 is excited and radiated by an ultraviolet ray generated upon plasma discharge to produce a red, green or blue color visible light ray. An inactive mixture gas, such as He+Xe or Ne+Xe, for a gas discharge is injected into a discharge space defined between the upper/lower substrate 10 and 18 and the barrier ribs 24.
Such a three-electrode AC surface-discharge PDP drives one frame, which is divided into various sub-fields having a different emission frequency, so as to realize gray levels of a picture. Each sub-field is again divided into a reset interval for uniformly causing a discharge, an address interval for selecting the discharge cell and a sustaining interval for realizing the gray levels depending on the discharge frequency. When it is intended to display a picture of 256 gray levels, a frame interval equal to {fraction (1/60)} second (i.e. 16.67 msec) in each discharge cell 1 is divided into 8 sub-fields SF1 to SF8 as shown in FIG. 2. Each of the 8 sub-field SF1 to SF8 is divided into a reset interval, an address interval and a sustaining interval. The reset interval and the address interval of each sub-field are equal every sub-field, whereas the sustaining interval and the discharge frequency are increased at a ration of 2n (wherein n=0, 1, 2, 3, 4, 5, 6 and 7) at each sub-field. Since the sustaining interval becomes different at each sub-field as mentioned above, the gray levels of a picture can be realized.
Such a PDP driving method is largely classified into a selective writing system and a selective erasing system depending on an emission of the discharge cell selected by the address discharge.
The selective writing system turns off the entire field in the reset interval and thereafter turns on the discharge cells selected by the address discharge. In the sustaining interval, a discharge of the discharge cells selected by the address discharge is sustained to display a picture.
In the selective writing system, a scanning pulse applied to the scanning/sustaining electrode 30Y has a pulse width set to 3 xcexcs or more to form sufficient wall charges within the discharge-cell.
If the PDP has a resolution of VGA (video graphics array) class, it has total 480 scanning lines. Accordingly, in the selective writing system, an address interval within one frame requires total 11.52 ms when one frame interval (i.e., 16.67 ms) includes 8 sub-fields. On the other hand, a sustaining interval is assigned to 3.05 ms in consideration of a vertical synchronizing signal Vsync.
Herein, the address interval is calculated by 3 xcexcs(a pulse width of the scanning pulse)xc3x97480 linesxc3x978(the number of sub-fields) per frame. The sustaining interval is a time value (i.e., 16.67 msxe2x88x9211.52 msxe2x88x920.3 msxe2x88x921 msxe2x88x920.8 ms) subtracting an address interval of 11.52 ms, once reset interval of 0.3 ms, and an extra time of the vertical synchronizing signal Vsync of 1 ms and an erasure interval of 100 xcexcsxc3x978 sub-fields from one frame interval of 16.67 ms.
The PDP may generate a pseudo contour noise from a moving picture because of its characteristic realizing the gray levels of the picture by a combination of sub-fields. If the pseudo contour noise is generated, then a pseudo contour emerges on the screen to deteriorate a picture display quality. For instance, if the screen is moved to the left after the left half of the screen was displayed by a gray level value of 128 and the right half of the screen was displayed by a gray level value of 127, a peak white, that is, a white stripe emerges at a boundary portion between the gray level values 127 and 128. To the contrary, if the screen is moved to the right after the left half thereof was displayed by a gray level value of 128 and the right half thereof was displayed by a gray level value of 127, then a black level, that is, a black stripe emerges on at a boundary portion between the gray level values 127 and 128.
In order to eliminate a pseudo contour noise of a moving picture, there has been suggested a scheme of dividing one sub-field to add one or two sub-fields, a scheme of re-arranging the sequence of sub-fields, a scheme of adding the sub-fields and re-arranging the sequence of sub-fields, and an error diffusion method, etc. However, in the selective writing system, the sustaining interval becomes insufficient or fails to be assigned if the sub-fields are added so as to eliminate a pseudo contour noise of a moving picture. For instance, in the selective writing system, two sub-fields of the 8 sub-fields are divided such that one frame includes 10 sub-fields, the display period, that is, the sustaining interval becomes absolutely insufficient. If one frame includes 10 sub-fields, the address interval becomes 14.4 ms, which is calculated by 3 xcexcs(a pulse width of the scanning pulse)xc3x97480 linesxc3x9710(the number of sub-fields) per frame. On the other hand, the sustaining interval becomes xe2x88x920.03 ms (i.e., 16.67 msxe2x88x9214.4 msxe2x88x920.3 msxe2x88x921 msxe2x88x921 ms) which is a time value subtracting an address interval of 14.4 ms, once reset interval of 0.3 ms, an erasure interval of 100 xcexcsxc3x9710 sub-fields and an extra time of the vertical synchronizing signal Vsync of 1 ms from one frame interval of 16.67 ms.
In such a selective writing system, a sustaining interval of about 3 ms can be assured when one frame consists of 8 sub-fields, whereas it becomes impossible to assure a time for the sustaining interval when one frame consists of 10 sub-fields. In order to overcome this problem, there has been suggested a scheme of divisionally driving one field. However, such a scheme raises another problem of a rise of manufacturing cost because it requires an addition of driver IC""s.
A contrast characteristic of the selective writing system is as follows. In the selective writing system, when one frame consists of 8 sub-fields, a light of about 300 cd/m2 corresponding to a brightness of the peak white is produced if a field continues to be turned on in the entire sustaining interval of 3.05 ms. On the other hand, if the field is sustained in a state of being turned on only in once reset interval and being turned off in the remaining interval within one frame, a light of about 0.7 cd/m2 corresponding to the black is produced. Accordingly, a darkroom contrast ratio in the selective writing system has a level of 430:1.
The selective erasing system makes a writing discharge of the entire field in the reset interval and thereafter turns off the discharge cells selected in the address interval. Then, in the sustaining interval, only the discharge cells having not selected by the address discharge are sustaining-discharged to display a picture.
In the selective erasing system, a selective erasing data pulse with a pulse width of about 1 xcexcs is applied to the address electrode 20X so that it can erase wall charges and space charges of the discharge cells selected during the address discharge. At the same time, a scanning pulse with a pulse width of 1 xcexcs synchronized with the selective erasing data pulse is applied to the scanning/sustaining electrode 30Y.
In the selective writing system, if the PDP has a resolution of VGA (video graphics array) class, then an address interval within one frame requires only total 3.84 ms when one frame interval (i.e., 16.67 ms) consists of 8 sub-fields. On the other hand, a sustaining interval can be sufficiently assigned to about 10.73 ms in consideration of a vertical synchronizing signal Vsync. Herein, the address interval is calculated by 1 xcexcs(a pulse width of the scanning pulse)xc3x97480 linesxc3x978(the number of sub-fields) per frame. The sustaining interval is a time value (i.e., 16.67 msxe2x88x923.84 msxe2x88x920.3 msxe2x88x921 msxe2x88x920.8 ms) subtracting an address interval of 3.84 ms, once reset interval of 0.3 ms, and an extra time of the vertical synchronizing signal Vsync of 1 ms and an entire writing time of 100 xcexcsxc3x978 sub-fields from one frame interval of 16.67 ms. In such a selective erasing system, since the address interval is small, the sustaining interval as a display period can be assured even though the number of sub-fields is enlarged. If the number of sub-fields SF1 to SF10 within one frame is enlarged into ten as shown in FIG. 3, then the address interval becomes 4.8 ms calculated by 1 xcexcs(a pulse width of the scanning pulse)xe2x88x92480 linesxe2x88x9210(the number of sub-fields) per frame. On the other hand, the sustaining interval becomes 9.57 ms which is a time value (i.e., 16.67 msxe2x88x924.8 msxe2x88x920.3 msxe2x88x921 msxe2x88x921 ms) subtracting an address interval of 4.8 ms, once reset interval of 0.3 ms, an extra time of the vertical synchronizing signal Vsync of 1 ms and the entire writing time of 100 xcexcsxc3x9710 sub-fields from one frame interval of 16.67 ms. Accordingly, the selective erasing system can assure a sustaining interval three times longer than the above-mentioned selective writing system having 8 sub-fields even though the number of sub-fields is enlarged into ten, so that it can realize a bright picture with 256 gray levels.
However, the selective erasing system has a disadvantage of low contrast because the entire field is turned on in the entire writing interval.
In the selective erasing system, if the entire field continues to be turned on in the sustaining interval of 9.57 ms within one frame consisting of 10 sub-fields SF1 to SF10 as shown in FIG. 3, then a light of about 300 cd/m2 corresponding to a brightness of the peak white is produced. A brightness corresponding to the black is 15.7 cd/m2, which is a brightness value of 0.7 cd/M2 generated in once reset interval plus 1.5 cd/M2xc3x9710 sub-fields generated in the entire writing interval within one frame. Accordingly, since a darkroom contrast ratio in the selective erasing system is equal to a level of 950:15.7=60:1 when one frame consists of 10 sub-fields SF1 to SF10, the selective erasing system has a low contrast. As a result, a driving method using the selective erasing system provides a bright field owing to an assurance of sufficient sustaining interval, but fails to provide a clear field and a feeling of blurred picture due to a poor contrast.
In order to overcome a problem caused by such a poor contrast, there has been suggested a scheme of making an entire writing only once per frame and taking out the unnecessary discharge cells every sub-field SF1 to SF10. However, this scheme has a problem of poor picture quality in that next sub-field can not be driven until the previous sub-field has been turned on and thus the number of gray levels becomes merely the number of sub-fields plus one. In other words, if one frame includes 10 sub-fields, then the number of gray level become eleven as represented by the following table:
 
In Table 1, xe2x80x98SFxxe2x80x99 means the x-numbered sub-field and xe2x80x98(y)xe2x80x99 expresses a brightness weighting value set for the subject sub-field as a decimal number y. Further, xe2x80x98Oxe2x80x99 represents a state in which the subject sub-field is turned on while xe2x80x98xxe2x80x99 does a state in which the subject sub-field is turned off.
In this case, since only 1331 colors are expressed by all combination of red, green and blue colors, color expression ability becomes considerably insufficient in comparison to true colors of 16,700,000. The PDP adopting such a system has a darkroom contrast ratio of 430:1 by a peak white of 950 cd/m2 when the entire field is turned on in the display interval of 9.57 ms and a black of 2.2 cd/m2 which is a brightness value adding 0.7 cd/m2 generated in once reset interval to 1.5 cd/m2 generate in once entire writing interval.
As described above, in the conventional PDP driving method, the selective writing system fails to make a high-speed driving because each of a data pulse for selectively turning on the discharge cells in the address interval and a scanning pulse has a pulse width of 3 xcexcs or more. The selective erasing system has an advantage of a higher speed driving than the selective writing system because each of a data pulse for selectively turning off the discharge cells and a scanning pulse is about 1 xcexcs, whereas it has a disadvantage of a worse contrast than the selective writing system because the discharge cells in the entire field is turned on in the reset interval, that is, the non-display interval.
Accordingly, it is an object of the present invention to provide a PDP driving method and apparatus that is capable of driving a PDP at a high speed as well as improving the contrast.
A further object of the present invention is to provide a PDP driving method and apparatus that is suitable for running a selective writing system compatible with a selective erasing system.
In order to achieve these and other objects of the invention, a PDP driving method according to one aspect of the present invention includes the steps of turning on discharge cells selected in an address interval using at least one selective writing sub-field; and turning off the discharge cells selected in the address interval using at least one selective erasing sub-field, wherein the selective writing sub-field and the selective erasing sub-field are arranged within one frame.
A PDP driving method according to another aspect of the present invention includes the steps of expressing a gray level range using at least one selective writing sub-field by turning on selected discharge cells and maintaining a discharge of the turned-on cells; and expressing a high gray level range using at least one selective erasing sub-field by successively turning off the cells turned on in the previous sub-field.
A PDP driving method according to still another aspect of the present invention includes a kth frame including at least one selective writing sub-field for turning on the discharge cells selected in an address interval and at least one erasing sub-field for turning off the discharge cells selected in the address interval; and a (k+1)th frame including at least one selective writing sub-field for turning on the discharge cells selected in the address interval and at least one erasing sub-field for turning off the discharge cells selected in the address interval and having brightness weighting values of the sub-fields different from said kth frame, wherein k is a positive integer.
A driving apparatus for a plasma display panel according to still another aspect of the present invention includes a first electrode driver for applying a first scanning pulse for causing a writing discharge and a second scanning pulse for causing an erasure discharge to a first electrode of said panel in the address interval in accordance with a sub-field to drive the first electrode; and a second electrode driver for applying a first data for selecting the turned-on cells and a second data for selecting the turned-off cells to a second electrode of said panel in such a manner to be synchronized with the scanning pulses, thereby driving the second electrode.
The driving apparatus for a plasma display panel further includes a third electrode driver for applying a desired direct current voltage to a third electrode of said panel in the address interval and applying a sustaining pulse for causing a sustaining discharge of the discharge cells selected in the address interval to the third electrode to thereby drive the third electrode.